Paula Wallis, TunnelTalk

Phase 1 of the 23 mile (37km) Silver Line of the Washington DC metro system, formerly the Dulles Corridor Metrorail, is set to celebrate a major milestone, and prequalifications for design-build realization of Phase 2 are expected to be called in the early New Year.

With the final lining of the twin tunnels connecting two of the stations in Tysons Corner now complete, the Phase 1 alignment is closer to its inauguration date. "There are a few small items to finish up, but by-and-large the tunnels have reached substantial completion," said Leslie Pereira, spokesperson for Dulles Transit Partners. "The inbound and outbound tunnels will be turned over to the track subcontractor shortly."

The short underground section comprises 1,700ft (518m) of twin tube NATM mined tunneling between a total 700ft (213m) of cut-and-cover work at the portals and a partially underground alignment for Tysons Central 7 Station (Fig 1).

Advanced as a PPP agreement with the Dulles Transit Partnership (a JV between Bechtel and the Washington Group), the 11.7 miles (18.8km) of Phase 1 extends the metro network from the East Falls Church Station on the existing Metro's Orange Line, through the financial and commercial area of Tysons Corner and on to the Wiehle Avenue Station (Fig 1).

"The design phase is 99% completed, while construction is about 60% completed," he said. "The aerial structure foundations are done, all of our piers are done, and most of our aerial structure is built."

Nowakowski said there are more than 1,700 workers on the project that will see greater activity in finishing the stations in the coming year to complete the Phase 1 works towards an opening of services on the extension in 2013.

While work continues on Phase 1, advance of Phase 2, to run from Wiehle Avenue Station to Dulles International Airport, is gearing up. "We have reached 100% of preliminary engineering for Phase 2, except for the portion to Dulles Airport, and we expect to finish that by February," he said. "We then expect to begin the requests for qualifications for Phase 2 design-build teams in January and conclude that process by the end of next year. Construction on the four to five year project could start in early 2013."

MWAA is managing construction and will operate and maintain the Silver Line once completed. Nearly 54% of the Silver Line cost will come from the airport toll road users, with another 5% coming from the State of Virginia; 16% in Federal grants; and the rest from Loudoun and Fairfax Counties.

Underground alignment selected over the elevated option for the Metrorail station at Dulles Airport

During a December 6 MWAA Board meeting, planners said Phase 1 is on time and on budget, with $1.58 billion of the $2.8 billion budget spent and another $54.1 million in the contingency fund. Bechtel, Metro and MWAA are in negotiations to decide who will pay for change orders, which will determine the final cost of Phase 1. Nowakowski said that, at the worst-case scenario, the overrun will be as much as $150 million.

In April 2011, MWAA selected an underground station at Dulles International Airport, but opted for a less expensive cut-and-cover station over the original NATM mined station and running tunnels to save $330 million on the original $3.83 billion estimate of the 12 mile (19.3km) Phase 2 extension.

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